A particular type of device in an emitter-switching configuration is provided by a high-voltage power switching element (for example, a bipolar transistor) and by a low-voltage signal switching element (for example, a bipolar or field-effect transistor). The emitter terminal of the high-voltage transistor is connected to the charge-collection terminal (the collector or drain) of the low-voltage transistor. Typically, the high-voltage transistor has an open-emitter collector-base breakdown voltage (Bv.sub.cbo) which may reach 2 kV, whereas the low-voltage transistor has a breakdown voltage below 60V. The rapid turn-off of the low-voltage transistor permits an extremely rapid turn-off of the high-voltage transistor and this configuration is, therefore, commonly used in applications in which the high-voltage transistor has to be able to switch rapidly between its conducting and cut-off states.
A device in an emitter-switching configuration includes a turn-off element provided, for example, by a diode connected between the base terminal of the high-voltage transistor and the charge-emitting terminal (the emitter or source) of the low-voltage transistor. During the opening of the device, the turn-off time of the high-voltage transistor is longer than the turn-off time of the low-voltage transistor because of the large accumulation of charge in the base region. After the low-voltage transistor has been turned off cancelling out the emitter current of the high-voltage transistor, the collector current of the high-voltage transistor therefore flows through its base and is discharged by the turn-off element, typically towards a reference terminal to ground. Once the high-voltage transistor has eliminated all of the residual charges in the base, this transistor is turned off and its collector current is brought to zero.